Support running VM tests under Windows

After the move to xtask to build/run/test the project, you can no longer run vm tests under Windows natively. While WSL2 can be used (and quite well), this feels like a regression.

Most of the incompatibility that I see off the bat is the usage of the `nix` crate to create pipes and possibly some filepath issues. Can anyone think of anything else that might be a bit of a roadblock?